The present invention relates to a process for the induction of normal rooting on nodal and internodal stem segments without using hormones and/or other chemical treatments in Mentha species. The invention more particularly provides a new and easy system of inducing normal roots on plant cuttings thereby leading to large scale production of propagules ready for field plantation of mints (Mentha species).
Mentha species, constitute not only the major essential oil crops of global significance but also serve as some of the chief culinary herbs. The essential oils extracted from the herb biomass is extracted through hydro-distillation. The volatile oil is a complex mixture of mainly monoterpenoids. The oils per se or their specific constituents find extensive use in a large cosmetic and pharmaceutical industries all over the world. Some of the highly functionalized monoterpenoidal constituents of the oil serve as novel synthagens for various chemcial industries. Different Mentha species serve as source of one or more of the popular natural phytochemicals like menthol, linalool, linalyl acetate, carvone, menthone etc. The ever increasing demand and utility of the oils or their specific constituents from the impetus of their increased significance as crops of choice for profitable agro-business. Furthermore, some of the species are as such consumed as ingredients of foods, spices and culinary herbal formulations etc. like Mentha piperita, Mentha virdis etc.
Many commercial Mentha species (e.g. Mentha arvensis, Mentha piperita) are propagated from subterranean suckers, stolons, etc. An area, preferably pertaining to the best land, of the previous crop is saved after second harvest (August) which during winter period produce underground suckers. In practice, in the months of January and February i.e., ending winters, the suckers are dug out, cut into about one inch pieces and directly planted in to the field and the new crop is irrigated immediately. The suckers thus sown take about 18 to 30 days to sprout (Kumar et al. 1997, CIMAPxe2x80x94Farm Bulletin Number 004). However, the xe2x80x98above ground canopyxe2x80x99 of the sucker-crop remains useless. It has never been explored for development of propagules concurrently for the new crop plantation. Thus, no state of the art already exists concerning the utilization and development of the aerial plant canopy as propagules for the plantation.
Rooting in mints and other plants under in vitro conditions is known to be induced by hormonal (auxins, IAA, IBA, NAA, BA, gibbrellins, cytokinin etc.) treatment and/or under culture media (e.g. MS medium, Murashige et al. 1962, Physiol. Plant. 15:473-497; LS medium, Linsmayer and Skoog 1965, Physiol. Plant 18:100-127) consisting of a number of ingredients including anions, cations, carbohydrates, nitrogenous compounds, vitamins, and singal metabolites like Ca2+, inositols etc. (Kukreja et al., 1991 J. Essential Oil Res. 4:623-629; Kukreja et al. 1992 Euphytica 53:183-192; Faure et al. 1998, Plant Cell Tissue and Organ Culture 52:204-212; Krasnyanski et al. 1998, Theor.App. Genet. 96:683-687, Rao et al. 1998, Plant Cell Rep. 17:861-865). The rooting in dicots, may also be induced by infective method i.e., with the help of Agrobacterium rhizogenes. However, the roots (so called xe2x80x98hairy rootsxe2x80x99) so obtained are not physiologically and genetically normal and native and behave differently (Banerjee et al., 1995, Curr. Res. Med. Aromatic Plants 17:348-378). Rooting in plant shoots and twigs have also been propagated under defined nutrient solutions like Hoagland Solutions, Johnsons Nutrient Solutions of various concentration-strengths have been used for long-term plant maintenance hydroponically and for root growth (Hoagland and Arnon, 1938 Circ. Calif. Agric. Exp. Stat. 347:32, Wickremesinhe and Arteca, 1994 Plant Sci. 101:125-135), however, rooting initiation under complete nutrient minus aqueous mileau has not come into knowledge hitherto. The patent hitherto (Driver, U.S. Pat. No. 4,612,725 dated Sep. 23, 1986; Wochok et al. U.S. Pat. No. 4,478,000 dated Oct. 23, 1984; Dobres et al U.S. Pat. No. 5,843,782 dated Dec. 1, 1998; Nishigori JP 7222536 dated Aug. 22, 1995) do not cover in vitro Rooting Induction (nodal and internodal) under the specified nutrient free conditions. The patent literature for plants in general and mints in particular lacks the method of rapid and direct induction of roots in stems, stem segments, multiple shoots etc. under complete nutrient free aqueous conditions invented herein. The xe2x80x98aerial rootsxe2x80x99 have not been produced and represent a new phenomenon of their induction through the invented process of treatment in mint species.
The invented protocol does not require special chemicals, hormones, micro organisms etc. for induction of rooting in stem, twigs or stem segments of Mentha species (Mentha citrata, Mentha piperita, Mentha cardiaca, Mentha spicata, Mentha arvensis, Mentha virdis, Mentha pulegium, and Mentha longifolia. The roots obtained by the invented protocol are genetically native and physiologically normal.
The method also provides a way to avoid exposure of the plant or plant part to numerous chemicals essentially supplemented in tissue culture media or nutrient solutions or other recipes/formulations of combinations of chemicals and hormones for bringing about rooting in vitro.
The invention is not only economically inexpensive but also technically feasible to be accomplished as and when desired with minimal infrastructural prerequisites. As a synergistic utility, the xe2x80x98above the groundxe2x80x99 canopy of the plants, besides the underground suckers, can be processed through the invented mode to produce rooted propagules to serve as plantlets for the new crop plantation. These propagules possess better and faster establishment behaviour to rapidly resume normal growth thereby offering agronomic advantage. Compared to 18 to 30 days required for sprouting of planted suckers, the root initiation in stem segments by the invention becomes visible within a week.
The juvenile roots could be particularly useful for the specialized physiological and biochemical studies concerning root-shoot interactions, ion uptakes and metabolic precursor feeding and transformations etc.
Additionally, it provides a way of producing rooting in tissue culture raised multiple shoots, required in biotechnological research as well as field transfer of the culture generated variants, clones, transformants etc.
The main object of the invention is to provide a process for the induction of normal rooting on nodal and internodal stem segments without using hormones and/or other chemical treatments in Mentha species which obviates the drawbacks of the earlier processes as detailed above.
Another object of the invention is to provide a new and easy system of rapid and production of normal roots in stem cuttings of Mentha species thereby leading to large scale production of propagule ready for the field plantation.
Still another object of the invention is producing aerial roots at the non-submerged inter-nodes of the twigs of Mentha species dipped in water under specified conditions.
In accordance with the above objectives, the invention provides a process for the induction of normal rooting on nodal and internodal stem segments without using hormones and/or other chemical treatments in Mentha species which comprises oblique excision of shoots of Mentha species from the plants, immediately dipping the cut end of twigs or stems into water and keeping in complete dark for up to one week with by varying the temperature cycle for each set of 24 hours duration of the treatment.
The invention discloses a process for the induction of normal roots on nodes and internodes of stem segments without using hormones and/or other chemical treatments in Mentha species. Mentha species, constitute not only the major essential oil crop of the global significance but also serves as some of the chief culinary herbs. The present invention is directed to, inter alia, a method of rapid ab initio induction of roots on the nodes and internodes of various Mentha species under nutrient as well as hormone minus aqueous system. The invented process involves applying specified duration of light and or dark treatments with temperature limit. The method allows use of above the ground canopy, of the mints to utilize as propagules for the fresh plantation using the rooted plantlets so generated. The invention provides a method to avoid exposure of the plant or plant parts to various chemicals essentially supplemented in tissue culture media or nutrient solutions or other recipes/formulations. The invention also provides a method of producing rooting in tissue culture raised multiple shoots, required in biotechnological research as well as field transfer of the culture generated variants, clones, transformants etc. and micropropagation purposes. Even xe2x80x98aerial rootsxe2x80x99 have also been produced as one of the facets of the invention. The invented process is a novel, fast convenient and inexpensive process for the induction of normal rooting in shoots, stems, twigs or stem segments as well as in tissue culture generated multiple shoots of Mentha species together with successful transplantation of the rooted plantlets for the new crop. A conceptual scientific explanation for the phenomena is proposed.
Accordingly, the present invention provides a process for the induction of normal rooting on nodal and internodal stem segments without using hormones and/or other chemical treatments in Mentha species which comprises oblique excision of shoots of Mentha species from the plants, immediately dipping the cut end of twigs or stems (with at least a pair of leaves) into water and keeping in complete dark for up to one week with temperature cycles of a range of 11-25xc2x0 C. for 11 hours and of a range of 5-10xc2x0 C. for 13 hours for each set of 24 hours duration of the treatment.
In an embodiment of the present invention the inflorescence head should be removed from the flowering twigs or shoots.
In another embodiment of the present invention the presence of a pair of leaves on the stem, stem segments, multiple shoots and twigs is mandatory for the induction of rooting
In yet another embodiment of the invention the source stems, shoots, twigs, stem segments etc. may be from the native plants growing in soil or from those produced in vitro through tissue culture techniques.
In yet another embodiment of the invention similar root induction may be achieved in certain other plants similar to mints like other Lamiacea, Bacopa monnieri etc.
In yet another embodiment of the invention the water may be replaced once or more times depending upon the rate of achieving root induction, leaching of terpenoidal constituents from the leaves or their putrefaction under water under certain circumstances (anaerobiosis etc.) could lessen or prevent rooting induction. However, aeration or replacement with fresh water could overcome the problem.
A light and dark dependent quantitative as well as qualitative differences in the rooting efficiency and rooting type phenomenon were observed with faster and more abundant rooting under complete dark treatment. As a phenomenally original observation out of the invention the root induction at even the non-submerged internodes (called herein as xe2x80x98aerial rootingxe2x80x99) in the stems or twigs with cut ends dipped in the water was observed only in the case of complete dark treatment.
Scientifically, the mandatory requirement of a pair of leaves for the induction of rooting may be because of their role in catering to the need of carbon and other nutrient to sustain the root growth. As such, it appears that the presence of a pair of leaves holds the secret of signal of rooting initiation with their subsequent role of the nutritional feeding of the initiated roots coming into picture subsequently. The fast and more abundant rooting in dark may be perceived along the same lines as dark treatment could set in the breakdown of storage or reserve starch in the leaves with the soluble carbohydrates thus generated provide abundant supply pool for translocation to the sink of rooting site. Again light-dark cycles could though periodically regulate the balance of starch-soluble carbohydrate production with the mobilization of starch during the intermittent dark period and replenishment of starch pool through photosynthetically generated transitory starch during the light period. It should imply that though rooting initiation and proliferation in light-dark cycles may be slower in rate, it may be temporally more sustainable under the no nutrient medium utilized in the invented process. A support to the above conceptual notion may be drawn from the fact that subterranean (underground) suckers which sprout to give full plants in conventional cultivation of propagation of the mints are thickened (xe2x80x98rhizomaticxe2x80x99) stolons having plenty of stored food to sustain sprouting (differentiation) and support early growth of the plantlets just like seed reserves do to the germinating embryos or like potato tuber portion do to the planted potato eyes. As concerns xe2x80x98aerial rootsxe2x80x99 induced under complete dark treatment of the invented process, a plausible explanation being postulated herewith is that such roots may be induced under severe depletion of nutrients (which are little available from the water as it is nutritionally un-supplemented and leaves progressively loose their status of higher gradient with progressive supply but no replenishment). Accordingly they may possess some special attribute to take up nutrients from air. It may be something like reminicient of the hanging roots in certain Ficus trees in nature. However, the concept speculated herewith needs experimental scrutiny of acceptance or rejection.
The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention.